1. Field of the Invention
The present invention relates to an antenna module built in a portable wireless terminal, and more particularly, to a built-in antenna module for improving performance of a variety of antennas, such as improving a radiation characteristic of a Planar Inverted-F Antenna (PIFA) and reducing a Specific Absorption Rate (SAR).
2. Background of the Prior Art
Recently, mobile wireless terminals, such as PCS, DCS, GPS, PDA, cellular phones and wireless notebooks, are growing in popularity; and terminals with various functions and designs are being introduced. Further, small-sized, slim and lightweight terminals are being introduced, and users expect such terminals to also support such various functions. Therefore, the design of the terminal is focused on reducing terminal size while maintaining or improving the functions, for customer satisfaction.
Specifically, a rod antenna (or whip antenna) or a helical antenna that is protruded outward from the terminal is easy to break when the terminal is dropped, and such antennas reduce the portability of the terminal. Therefore, a plate type antenna installed within the terminal is widely used in recent days (also called a built-in antenna, internal antenna, or intenna) and various efforts are made to improve the performance and productivity of the built-in antenna.
Generally, the above-described built-in antenna is electrically connected to a mainboard (RF board) of a terminal body. At this time, the built-in antenna has two feeding lines. One line is electrically connected to a feeding unit of the mainboard, and the other line is grounded to a conductive ground layer of a multi-layered mainboard for operation. At this time, the ground layer is positioned at an uppermost layer of the mainboard, and the plate type built-in antenna (radiator) is grounded with only a grounding unit. The feeding unit is lead-out downwardly to a distance of a predetermined height from the mainboard by use of a fixing bracket. Generally, a Planar Inverted F Antenna (PIFA, a plate type built-in antenna) has improved performance when the size of a radiator, the area of a ground surface and the height between the radiator and the ground surface are increased.
However, a conventional feeding structure of the built-in antenna has a drawback in that a larger distance between the PIFA and the ground surface of the mainboard goes against consumer's desire for slimness of the portable terminal and simplification. Accordingly, recent slide type terminals being put on a market, have deteriorated antenna performance.